The Braves have traded Kotsay to the Red Sox in exchange for Minor League outfielder Luis Sumoza.
Kotsay was expected to be in uniform at Yankee Stadium in time for Wednesday night's game between the Yankees and Red Sox, though he was not in the starting lineup.
"To be with the Red Sox will be cool," Kotsay said. "I've always said there were a couple of teams I'd like to play for, with Atlanta being one of them. But I'm looking forward to joining the Red Sox and being in the pennant race."
After being acquired by the Braves in a January trade with the A's, Kotsay provided the veteran presence Atlanta envisioned. In 88 games this year, the 32-year-old outfielder hit .289 with six homers and 37 RBIs.
With J.D. Drew on the disabled list, Kotsay should see regular time with the Red Sox in right field and center field.
Sumoza hit .301 with 11 homers and a .539 slugging percentage with the Class A Lowell Spinners this season. The 20-year-old outfielder has enjoyed a productive August, hitting .354 with five homers.
Mark Bowman is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.